Check the version of ldiscn32.exe on your client machine. Is it 9.60.1.0? I'm using the latest component patch so my version is 9.60.2.111. It appears that there is a mismatch between the scanner (ldiscn32.exe) and the database. Look inside the scan file in ErrorScan and search for the line
Security - Antivirus Software - Antivirus
You should see something like
Security - Antivirus Software - Antivirus - (Number: 0) - Product Name =<some product name>
My guess is that you're either missing the (Number) portion, or you're missing the actual number (Number:). Number is the unique identifier for AntiVirus. Based on the error above, the inventory service isn't finding a value for "number" in your scan file, so it's leaving it blank, resulting in a NULL. That's not valid, so you get the exception.
1. Verify your scanner on your client is up-to-date. If it isn't, redeploy your client. Make sure that the version of ManagementSuite\LDLogon\ldiscn32.exe on your core matches the version on your client.
2. Find the lines in your scan file and paste them in a reply, along with the version of the ldiscn32.exe from your client. The Date Created and Date Modified would be helpful as well as the File Size.